Auto-Focus Methods and Systems for Multi-Spectral Imaging

ABSTRACT

Techniques for acquiring focused images of a microscope slide are disclosed. During a calibration phase, a “base” focal plane is determined using non-synthetic and/or synthetic auto-focus techniques. Furthermore, offset planes are determined for color channels (or filter bands) and used to generate an auto-focus model. During subsequent scans, the auto-focus model can be used to quickly estimate the focal plane of interest for each color channel (or filter band) rather than re-employing the non-synthetic and/or synthetic auto-focus techniques.

TECHNICAL FIELD

The technology disclosed herein relates to computer-based systems forimaging microscope slides and auto-focus techniques.

BACKGROUND

Digital pathology equipment is often used to produce digital images ofmicroscope slides. Pathologists and histotechnologists often visuallyexamine the digital images to obtain information about tissue samplesand to identify the most appropriate treatment to improve a clinicaloutcome. To produce color images, automated slide scanners often acquireimages in each of red, green, and blue color (RGB) channels and combinethe images to produce a RGB image. Scanners also acquire a plurality ofimage channels with different spectral characteristics, like e.g.fluorescence imagers with a bench of multiple or tunable filters toacquire image data. In order to achieve suitable image data, automatedslide scanning often includes automatically scanning a tissue sample ata large number of different Z-planes. Many of the captured imagesprovide little or no value because the image data is often out of focusin most of the Z-planes. This problem also affects fluorescence imagingusing a filter bench.

Additionally, the Z-plane for the best focus in the blue or green colorchannel may not be the Z-plane for the best focus in the red colorchannel, especially if the features being imaged are small (for example,less than 20 times the wavelength of light). Image blur in one colorchannel can impair the overall color image quality leading to seriousproblems with interpretation, diagnosis, and/or automated imageanalysis. To reduce blur, color slide scanners can acquire a completeZ-stack of images (e.g., a set of Z-stack of images for each colorchannel) and use complex auto-focus algorithms to create a single imagefrom the Z-stacks. Unfortunately, this requires significant Z-stackacquisition time, memory to store a large amount of Z-stack data, andsignificant processing time to analyze the Z-stack data and to generatethe color image. Alternatively, conventional color slide scanners canselect a focus (or focal) plane for one channel and then scan otherchannels at the selected focus plane. For example, a focus plane can beselected for the best focus of the green channel. The slide scanneracquires images in the red and blue channels at that focus plane toproduce a color or multi-spectral image. Unfortunately, the common focusplane used for all of the channels may not be the best focus plane foreach channel, resulting in unwanted image blur in the composite imagefor features that are dominated by colors other than the one thatdominated the focusing procedure.

Overview of the Technology

At least some embodiments of the disclosed technology are imagingsystems that enhance the focus of composite images by capturing imagesat focal planes selected to improve the balance between opticalsharpness, color separability and human readability. Each channel (e.g.,a color channel) or filter band of a digital imager device can have adifferent focal plane. The “in focus” focal planes can be selected tocapture a limited number of images (e.g., one image per channel orfilter band) to produce a composite image that is most optimally focusedfor all color channels while limiting imaging times, data storage, orthe like. The imaging system can produce, for example, highly-focusedcolor images of a specimen by combining individual images in differentcolor channels obtained at respective focal planes.

The focal plane or “in focus” Z-slice can correspond to captured imagesin a channel (or filter band) with the least amount of blur, sharpestimage, etc. Each color channel (or filter band) is captured using anoptimal focal plane or Z-slice for that color channel (or filter band)to limit or substantially reduce the amount of blur and/or distortion(e.g., chromatic aberration) observed in the composite image. Theimaging systems can image one or more calibration microscope slides(e.g., phantom slides, tissue-specific training slides, etc.) indicativeof, for example, tissue characteristics of tissue samples from patients.The imaging system can analyze the acquired images of the calibrationslides to evaluate, for example, distortion, color aberration, or otherunwanted problems. In some calibration processes, the impact of coloraberration or distortion between a single auto-focus plane for all colorchannels and the best individual focal plane for each color channel isdetermined.

The imaging system can use model fitting techniques to processsubsequent fields of views of the same tissue sample or different tissuesamples. The model fit can be an offset or fitting technique involving,for example, polynomial fitting or other suitable fitting of a positionof a specimen and a channel or band focal plan as variables. In somecalibration processes, a Z-stack of images of one or more calibrationslides can be obtained. The imaging system can determine the focal planefor each channel or filter band and compare that focal plane to apredicted focal plane from an auto-focus algorithm. This information isprovided to the focus method applied when imaging an object like tissue,cells, etc. The information and, therefore, the auto-focus algorithm canbe continuously or periodically updated based on the comparison toincrease the accuracy of the auto-focus algorithm. In some embodiments,the auto-focus algorithm is updated based on a comparison of images at apredicted focal plane and an actual in-focus focal plane. The comparisonof images in one channel can be used to select focal planes in otherchannels. Thus, two images in a single channel can be used to determineoptimal focal planes in additional channels. Additionally, auto-focusalgorithms of one channel can be adjusted based on an adjustment (e.g.,focusing) of another channel. This can reduce overall processing timeand enhance image quality.

In some embodiments, a multi-spectral computer-based system acquiresfocused color images of a microscope slide. In a calibration step, thesystem determines a Z-offset from a reference focus plane for one ormore color channels of a color digital imager. The one or more referencefocus planes can be, for example, the best focus plane individuallyselected for each color channel in a subset of color channels in thefinal image. In a scanning step, the system can determine a best focusplane for a field of view of the color digital imager. The color digitalimager can obtain image data in the field of view in one or more of thered, green and blue color channels in accordance with the Z-offsetsdetermined in the calibration step. Also, different routines can beperformed to individually auto-focus each color channel, and methods toauto-focus can be selected based on an application and imaged tissue athand.

In some embodiments, a method for acquiring focused images of amicroscope slide can be performed using a microscope having an opticalsystem and a digital color camera. The method includes characterizingchromatic aberration present in the optical system as a Z-offset from abest focus plane in each of the red, green and blue color channels ofthe digital color camera. The microscope slide can be imaged in a mannerto reduce the effect of the characterized chromatic aberration byobtaining image data from the red, green and blue color channels inaccordance with the Z-offsets. A multi-spectral system can includememory storing instructions that can be executed to automatically focusthe optical system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a computer-based system and environment forperforming auto-focus techniques in accordance with an embodiment of thedisclosed technology.

FIG. 2 is a block diagram illustrating a facility for enhancingauto-focus routines in accordance with an embodiment of the disclosedtechnology.

FIG. 3 is a flow diagram illustrating processing of a calibratecomponent in accordance with an embodiment of the disclosed technology.

FIG. 4 is a flow diagram illustrating processing of a Z-calibratecomponent in accordance with an embodiment of the disclosed technology.

FIG. 5 is a flow diagram illustrating processing of a scan component inaccordance with an embodiment of the disclosed technology.

FIG. 6 is a flow diagram illustrating processing of a Z-scan componentin accordance with an embodiment of the disclosed technology.

FIG. 7 is a block diagram illustrating processing of a test component inaccordance with an embodiment of the disclosed technology.

FIGS. 8A-8E are display images at various Z-slices or focal planesgenerated for a particular slide in accordance with an embodiment of thedisclosed technology.

DETAILED DESCRIPTION

At least some embodiments of the disclosed technology are imagingsystems that include a facility configured to improve the “sharpness” ofcaptured images by capturing images at different focal planes and/orZ-slices (e.g., Z-planes generated by a Z-stacking or focal planemerging process) for different color channels or filter bands. For eachcolor channel or filter band, the facility identifies the focal plane orZ-slice having the least amount of blur (i.e., the focal plane orZ-slice that is “most in focus”) and uses these focal planes orZ-slices, for example, to capture focused images. The focused images canbe combined to produce a focused composite image. For example, a focusedred channel image, a focused green channel image, and a focused bluechannel image can be combined to produce a focused color image. Becausethe facility uses an optimal focal plane or Z-slice for each colorchannel (or filter band), the amount of chromatic aberration observed inthe final composite image can be reduced.

It should be noted that although it is typical for those skilled in theart of microscopy and digital imaging to speak of the “sharpness” of theimage or the sharpness of the focus, we would like to emphasize in thispatent that the “best focus” is not necessarily the “sharpest”. Often itis better to optimize color separability or human readability in somecombination with optical or focal sharpness. Therefore, by “sharper” and“sharpest”, the inventors mean “more optimal” or “optimum” in the senseof balancing optical sharpness, color separability and humanreadability. “Human readability” is included because often the image iseasier to interpret if some of the fine structure (tissue structure thatis irrelevant to the diagnosis) of the specimen is not so evident andthis can be included in the model that is identified in the patent.

The techniques described herein can be used to enhance known auto-focusand Z-slicing techniques, such as passive or active auto-focustechniques including, but not limited to, phase detection auto-focustechniques, contrast detection auto-focus techniques, and so on.Additional auto-focus, Z-slicing, and slide imaging techniques aredescribed by Bradley and Bamform in “A One-pass Extended Depth of FieldAlgorithm Based on the Over-complete Discrete Wavelet Transform”; Imageand Vision Computing ‘04 New Zealand (IVCNZ'04), Akaroa, New Zealand,pp. 279-284 (November 2004); U.S. Non-Provisional patent applicationSer. No. 13/697,681, filed May 4, 2011, entitled “Autofocus Imaging”;U.S. Provisional App. No. 61/367,341, filed Jul. 23, 2010, entitled“On-the-Fly Focusing Sensor”; U.S. Provisional App. No. 61/299,231,filed Jan. 28, 2010, entitled “Slide Caching in a Slide ScanningMicroscope”; U.S. Provisional Application No. 61/261,251, filed Nov. 13,2009, entitled “Scanning Microscope Slide Stage”; U.S. Provisional App.No. 61/256,228, filed Oct. 29, 2009, entitled “High Speed Slide ScanningSystem for Digital Pathology”; U.S. Provisional App. No. 61/252,995,filed Oct. 19, 2009, entitled “On-the-Fly Focusing Systems andTechniques for Scanning Microscopes”; and U.S. Pat. No. 7,200,252, filedOct. 28, 2012, entitled “Color Space Transformations for Use inIdentifying Objects of Interest in Biological Specimens”.

In some embodiments, the facility generates an auto-focus model during acalibration phase or step and uses the generated auto-focus model duringsubsequent scans of slides and/or field of view scans to reduce scantime and data size while providing improved focus for each individualcolor channel (or filter band). During the calibration step, thefacility determines a “base” auto-focus plane or Z-slice for one imageand then determines auto-focus plane “offsets” for various colorchannels (or filter bands). The calibration step includes analyzing oneor more “phantom” or “training slides” that are representative ofspecimens (e.g., bacteria, biological material, and so on), tissue(e.g., breast tissue, tumor tissue, and so on), or other specimens to bescanned. A “base” value is determined by applying an auto-focustechnique to the training slide(s) by analyzing images of the slide(s)captured at different focal planes. One of ordinary skill in the artwill recognize that many different auto-focus algorithms may beemployed, including those mentioned above and other auto-focustechniques. The “base” value, in some embodiments, is generated usinggray scale version of the slide(s). In other embodiments, the “base”value is generated using a single color channel, a combination of colorchannels (e.g., a combination of color channels which may be dominatedby a single color channel such as green), a single filter band,luminosity values, and so on. The calibration step can further includedetermining an “offset” value in Z for each color channel (or filterband) corresponding to the focal plane offering the highest degree ofsharpness for the color channel (or filter band). The facility candetermine each “offset” value by applying an auto-focus technique to afirst slide by analyzing color channel or filter band-specific images ofthe slide(s) captured at different focal planes (or different Z-slices)to identify the sharpest focal plane (or Z-slice). Each “offset” valuecan be calculated as a difference from the “base value.” For example, ifthe “base” value is at a Z of 23 μm (micrometers) and the sharpest focalplane for a red color channel is at a Z of 24 μm, then the red colorchannel offset is +1 μm. As another example, if the “base” value is 25μm and the sharpest focal plane for a red color channel is 24 μm, thenthe red color channel offset is −1μm. As another example, if a “base”Z-slice has an index of 7 and sharpest Z-slice for a red color channelhas an index of 9, then the red color channel offset is +2. In someembodiments, the base value may correspond to measure of the lensrelative to its overall range of movement. For example, if the lens hasan overall range of movement of 50 μm, the base value may represent ameasure between 0 μm and 50 μm along the overall range of movement. Whenmultiple training slides are used, the resulting base and offset valuescan be combined into a single composite model by, for example, computingthe average base and offset values for each slide position/color channel(or filter band), using the most common base and offset values, or othersuitable aggregation techniques.

In some embodiments, the facility divides slide data into a grid (e.g.,1×1, 3×3, 9×9, 12×24, 100×1000, etc.) and performs the calibration stepfor each section of the grid. For example, if the facility divides slidedata into a 3×3 grid, the facility generates one “base” value for eachof the 9 sections and generates one offset value for each color channelor filter band for each of the 9 sections. In this manner, the model canbe optimized for each section of the grid. The “base” values may becalculated using, for example, a gray scale version of the capturedimage data, luminosity values for the captured image data, a singlecolor channel of the captured image data (e.g., red, green, blue), aparticular filter band, and so on.

In some embodiments, the facility creates calibration data by invokingan existing auto-focus algorithm during a calibration phase with, forexample, a suitable phantom slide or set of tissue-specific trainingslides (i.e., calibration slides) reflective of the tissue structuralvariability for the independent color channels (or filter bands). Thefacility may also invoke an existing single-channel auto-focus methodand compare the results to the enhanced auto-focus method to determinethe impact of chromatic aberration as differences between single-planeauto-focus and each individual best focus plane. A model fit (e.g., anoffset or polynomial fitting using the slide position and color channel(or filter band) as variables) can be employed while scanning slidesafter calibration.

In certain embodiments, the facility creates calibration data from aZ-slice scan of a suitable phantom slide and determines the Z-slice withbest focus individually for each color channel (or filter band) andcompares this to the result of the auto-focus algorithm applied to thesame slide to generate an offset value that can be applied tosubsequently scanned slides. In some embodiments, the facility appliesthis calibration technique to the subsequently-scanned slides andcompares the calibration information to previously-generated models todetermine whether the models need to be updated.

At least one of the color channels can be acquired at the “base”auto-focus plane or Z-slice determined for the slide without an offset.Therefore, at least one color channel is imaged at the standard focusplane and with the focus plane modified by applying an offset asdiscussed above. For each color channel, a focus sharpness metric can becomputed for the two focal planes or Z-slices acquired and the optimalplane (i.e., sharpest) can be selected for output. Appropriate focussharpness optimization metrics can be based on some computation derivedfrom or related to the gradient of image intensity in the x-directionand y-direction of an image. In one embodiment, the computation of sucha metric can be performed by translating the image a few pixels inx-direction and/or y-direction and summing the absolute differences.More complex focus optimized metric algorithms (including, for example,application-specific measures of focus sharpness) are frequently used toenhance the contribution to this computation from one type of feature(such as dots, corners, lines, ridges, plateaus or other shapes commonto the images under consideration) over others. A review of focussharpness (traditional “sharpness”) metrics can be found in S. Pertuz,D. Puig, M. Angel Garcia, “Analysis of focus measure operators forshape-from-focus,” Pattern Recognition, Volume 46, Issue 5, May 2013,Pages 1415-1432, where they are referred to as “focus measureoperators”. Another method for computing a generalized focus sharpnessmetric is to carry out a median filter operation or other type of imagesmoothing on a monochrome image representing one color channel of theimage or a combination of the color channels available in the image.After such a filter, the smoothed image can be subtracted or otherwisecombined with the original to yield a scalar, vector or matrix that withhigher absolute values when the image is in focus and lower absolutevalues when it is out of focus. Summing the absolute difference of thetwo images is one example of such a combining method. Extending this,the median filter can be carried out in parallel multiple times,increasing the local application of the filter from 3×3 pixels to 5×5pixels to 7×7 pixels, etc. The values corresponding to the maxima (orany other measure of intensity) in the resulting images, sometimesincluding the original, can be fit to a straight line or combined insome other way that characterizes the sequence of values. For an imagethat is in sharp focus, the slope of such a line is greater than theslope for an image that is not in sharp focus. Thus, with the scanacquisition process, no more than two images are acquired for an imagedslide while focus performance will show no loss over standard auto-focustechniques. This additional automatic quality assurance technique can beused, for example, when experiments indicate a risk for image qualitydegradation for some of the modified acquisitions. In some embodiments,the facility automatically updates the model parameters for thecorrection of chromatic aberration of the auto-focus algorithm if theabove-mentioned automatic quality assurance technique fails. A robustupdate scheme (e.g., a weighted match of previous and currentobservation or the search of an optimal setting for the last N Z-slicescans) can be employed, if needed or desired.

FIG. 1 illustrates a computer-based system and environment for analyzingtissue specimens in accordance with an embodiment of the disclosedtechnology. An analyzing system 100 includes an imaging apparatus 110and client computer systems 120. Specimen-bearing microscope slides canbe loaded into the imaging apparatus 110. The imaging apparatus 110 canperform auto-focus techniques and produce images of the specimens inmultiple color channels. In some embodiments, the imaging apparatusincludes a microscope for bright field and/or fluorescent imaging of thespecimen-bearing microscope slides. The imaging apparatus 110 mayfurther be a whole-slide scanner. One example whole-slide scanner is theVENTANA iScan HT product of the assignee Ventana Medical Systems, Inc.(Tucson, Ariz.). The images can be sent to the client computer systems120 either through a direct connection (not shown) or via a network 130.The client computer systems 120 display images to users, such aspathologists, histotechnologists, or the like.

The imaging apparatus 110 can include, without limitation, one or moreimage capture devices 111 and facilities 200. Internal components of theimaging apparatus 110 are shown in phantom line. Image capture devices111 can include, without limitation, a digital imager 113 (e.g., adigital camera) with an optical system (e.g., one or more lenses 115,sensor focus lens groups, microscope objectives, etc.), imaging sensors(e.g., a charge-coupled device (CCD), a complimentary metal-oxidesemiconductor (CMOS) image sensor, or the like), or the like. In digitalembodiments, the digital imager 113 can include a plurality of lensesthat cooperate to provide focusing (e.g., auto-focusing). A CCD sensorcan capture a digital image of specimen slide 117. In some embodiments,the digital imager 113 has red, green and blue color channels forproducing color images and is operable to capture images at differentfocal planes or Z-slices. In other embodiments, the digital imager 113is a monochromatic or color sensor, the optical system includes multipleand/or tunable filters, and multispectral or color image channels arecreated by acquiring multiple images from imager 113 with differentfilters and/or filter settings. One method of producing a color imageincludes determining one or more scan areas comprising a region or slideposition of the microscope slide that includes at least a portion of thespecimen. The scan area may be divided into a plurality of snapshots. Animage can be produced by combining the snapshots. The combined image ofthe whole specimen or slide can have snapshots with images in the RGBchannels at the same or different focal planes. The imaging apparatus110 can also include an access door 121 and a controller 123. Slide canbe loaded into the imaging apparatus 110 via the access door 121, andthe controller 123 can be used to control operation of the imagingapparatus 110.

The imaging apparatus 110 and client computer systems 120 can include adesktop computer, a laptop computer, a tablet, or the like and caninclude digital electronic circuitry, firmware, hardware, memory, acomputer storage medium, a computer program, a processor (including aprogrammed processor), or the like and can store digital images inbinary form. The images can also be divided into a matrix of pixels. Thepixels can include of a digital value of one or more bits, defined bythe bit depth. The digital value may represent, for example, energy,brightness, color, intensity, density, elevation, or a classified valuederived through image processing. Non-limiting exemplary digital imageformats include, but are not limited to, bit-mapped, joint picturesexpert group (JPEG), tagged image file format (TIFF), and graphicsinterchange format (GIF), as well as other digital data formats.

The network 130 or a direct connection interconnects the imagingapparatus 110 and the client computer systems 120. The network 130 mayinclude, without limitation, one or more gateways, routers, bridges,combinations thereof, or the like. The network 130 may include one ormore servers and one or more websites that are accessible to users andcan be used to send and receive information that the client computersystems 120 can utilize. A server may include, without limitation, oneor more associated databases for storing information (e.g., digitalimages, algorithms, staining protocols, or the like). The network 130can include, but is not limited to, data networks using the TransmissionControl Protocol (TCP), User Datagram Protocol (UDP), Internet Protocol(IP) and other data protocols. The client computer systems 120 canperform the methods and techniques discussed herein. Components andfeatures of the client computer system 120 can be mixed and matched withother components and features of the disclosed technology.

FIG. 2 is a block diagram illustrating a facility 200 for enhancingauto-focus routines in some embodiments. The facility 200 comprisescalibrate component 210, Z-calibrate component 220, scan components 230,240, test component 250, slide data store 260, and model store 270. Thefacility can selectively invoke the calibrate component 210, Z-calibratecomponent 220, scan components 230, 240, and/or test component 250. Thecalibrate component 210 calibrates and generates a focal plane-basedauto-focus model that can be applied to subsequently scanned slides. TheZ-calibrate component 220 calibrates and generates a Z-slice-basedauto-focus model that can be applied to subsequently scanned slides. Thescan component 230 can scan and generate images using a focalplane-based auto-focus model generated by the calibrate component 210.The Z-scan component 240 can scan and generate images using aZ-slice-based auto-focus model generated by the Z-calibrate component210. The test component 250 determines whether a previously-generatedmodel needs to be updated and, if so, updates the model. Slide datastore 260 stores captured slide data (e.g., images, such as Z-slices,metadata, and so on). Model store 270 stores model information, such asbase values and offset values for different slide positions anddifferent slide data types. For example, the model store 270 may includedifferent models for different types of tissue or other imaged data.

FIG. 3 is a flow diagram illustrating the processing of the calibratecomponent 210 of FIG. 2 in accordance with some embodiments. Thecalibrate component 210 may be invoked for a single training slide or aseries of training slides to generate an auto-focus model. In block 305,the component determines a slide position or positions for the slide.For example, if the component is configured to generate values for aparticular grid configuration, the component identifies the area orareas of the slide corresponding to sections of the grid. In someembodiments, the component may prompt a user to identify the slidepositions.

In blocks 310-345, the component loops through each of the determinedslide positions to generate base and offset values for each slideposition. In block 315, the component invokes an auto-focus technique toidentify an in-focus focal “base” plane for the current slide and storesan indication of the focal plane (e.g., a distance from the lens orother portion of the imaging apparatus to the focal plane) and slideposition. In some embodiments, the base plane may be determined byanalyzing gray scale images of the slide. In other embodiments, the baseplane may be determined by analyzing a particular color channel (orfilter band). In blocks 320-340, the component loops through each colorchannel (or filter band) to determine an offset value for each colorchannel (or filter band). In block 325, the component invokes anauto-focus technique to identify an in-focus focal plane for thecurrently selected color channel (or filter band) and slide position.For example, the in-focus plane can be determined based on a distancefrom the lens or other portion of the imaging apparatus to the focalplane. In block 330, an offset for the currently selected color channel(or filter band) is determined based on the distance between the focalplanes identified in blocks 325 and 315. In block 335, the componentstores the determined offset. In block 340, the next color channel (orfilter band), if any, is selected and the component then loops back toprocess the next color channel (or filter band). In block 345, thecomponent selects the next slide position, if any, and then loops backto process the next slide position.

In block 350, an auto-focus model is generated using the base and offsetvalues determined for each slide position. The auto-focus model stores,for example, an indication of the number and location of slidepositions, an indication of the type of material scanned (e.g., breasttissue, bacteria, etc.), a base value for each slide positioncorresponding to the base focal plane and, for each color channel orfilter band, one offset value for each slide position. Table 1 providesan example of the type of data that may be stored in a model generatedfor tissue using a 3×3 grid layout.

TABLE 1 Breast Tissue (3 × 3) offset_(red) = −2.0 μm offset_(red) = 1.2μm offset_(red) = 2.4 μm offset_(green) = −1.7 μm offset_(green) = 2.1μm offset_(green) = −1.2 μm offset_(blue) = 0.4 μm offset_(blue) = −0.7μm offset_(blue) = 1.1 μm offset_(red) = −3.0 μm offset_(red) = 2.0 μmoffset_(red) = −1.9 μm offset_(green) = 1.0 μm offset_(green) = −1.3 μmoffset_(green) = 2.0 μm offset_(blue) = 0.6 μm offset_(blue) = −1.1 μmoffset_(blue) = −1.1 μm offset_(red) = 0.9 μm offset_(red) = −0.3 μmoffset_(red) = 0.8 μm offset_(green) = 1.2 μm offset_(green) = 1.0 μmoffset_(green) = −2.4 μm offset_(blue) = −1.9 μm offset_(blue) = −1.1 μmoffset_(blue) = −3.0 μm

In this example, the model includes nine red channel offsets (offset_(red)), nine green channel offsets (offset_(green)), and nine bluechannel offsets (offset_(blue)), one of each for each slide position. Insome embodiments, the model may also store an indication of the type ofimages that were used to determine the base focal plane (e.g., grayscaleimage, a particular filter band, a particular color channel). Althoughthe data stored in Table 1 is shown in a format that is readilyinterpreted by a human, one skilled in the art will recognize that thedata may be stored in any manner or data structure.

FIG. 4 is a flowchart illustrating the processing of a Z-calibratecomponent 220 to calibrate and generate a Z-slice-based auto-focusmodel, in accordance with some embodiments. The component 220 may beinvoked by the facility 200 for a single training slide or a series oftraining slides to generate an auto-focus model. In block 405, thecomponent generates Z-slices for the slide using any focus stackingtechnique. In some embodiments, the component may retrieve storedZ-slices generated from previously captured slide data. In this manner,the disclosed techniques can be used to enhance the auto-focus ofpreviously-captured slides. In block 410, a slide position or positionsfor the slide can be determined. For example, if the component isconfigured to generate values for a particular grid configuration, thecomponent identifies the areas of the slide corresponding to sections ofthe grid. In some embodiments, a user is prompted to identify the slidepositions. In blocks 415-450, the component loops through each of thedetermined slide positions to generate base and offset values for eachslide position. In block 420, Z-slices are analyzed to identify theZ-slice having the sharpest image by, for example, using known focusstacking techniques. In some embodiments, the base Z-slice may bedetermined by analyzing gray scale version of each Z-slice. In otherembodiments, the base Z-slice may be determined by analyzing aparticular color channel or filter band. In blocks 425-445, thecomponent loops through each color channel (or filter band) to determinean offset value for each color channel (or filter band). In block 430,the Z-slice having the sharpest image for the current color channel isidentified. In block 435, an offset for the currently selected colorchannel (or filter band) is determined based on the difference betweenthe Z-slices identified in blocks 420 and 430. In block 440, thecomponent stores the determined offset. In block 445, the next colorchannel (or filter band), if any, is selected and the component thenloops back to process the next color channel (or filter band). In block450, the component selects the next slide position, if any, and thenloops back to process the next slide position. In block 455, anauto-focus model is generated using the base and offset valuesdetermined for each slide position. The auto-focus model stores, forexample, an indication of the number and location of slide positions, anindication of the type of material scanned (e.g., breast tissue,bacteria), a base value for each slide position corresponding to thebase Z-slice and, for each color channel or filter band, one offsetvalue for each slide position. Table 2 provides an example of the typeof data that may be stored in a model generated for tissue using a 3×3grid layout.

TABLE 2 Breast Tissue (3 × 3) - Z-slices = {0 . . . 15} offset_(red) = 1offset_(red) = 5 offset_(red) = −1 offset_(green) = −3 offset_(green) =−3 offset_(green) = 0 offset_(blue) = 4 offset_(blue) = 3 offset_(blue)= 1 offset_(red) = −3 offset_(red) = 2 offset_(red) = 0 offset_(green) =3 offset_(green) = −4 offset_(green) = −2 offset_(blue) = −2offset_(blue) = 4 offset_(blue) = 0 offset_(red) = −4 offset_(red) = 3offset_(red) = −1 offset_(green) = 1 offset_(green) = 2 offset_(green) =2 offset_(blue) = −3 offset_(blue) = −3 offset_(blue) = −2

In this example, 16 Z-slices were generated and each Z-slices isidentified by an index from 0 to 15. Furthermore, the model includesnine red channel offsets (offset _(red)), nine green channel offsets(offset_(green)), and nine blue channel offsets (offset_(blue)), one ofeach for each slide position. In some embodiments, the model may alsostore an indication of the type of images that were used to determinethe base focal plane (e.g., grayscale image, a particular filter band, aparticular color channel). Although the data stored in Table 2 is shownin a format that is readily interpreted by a human, one skilled in theart will recognize that the data may be stored in any manner or datastructure.

FIG. 5 is a flow diagram illustrating the processing of the scancomponent 230 of FIG. 2 for capturing images of a slide based on theauto-focus model, in accordance with some embodiments. In block 505, thecomponent determines slide positions based on the model. Using the modelof Table 1 as an example, the component may identify the portions of theslide corresponding to each position in the 3×3 grid by splitting theslide into 9 portions corresponding to the 3×3 grid. In someembodiments, the model may include additional information about thelocation of each portion if, for example, the portions are not the samesize, which the scan component may use to determine the slide positions.In blocks 510-550, the component loops through each of the determinedslide positions to capture one or more images for each slide position.In block 515, auto-focus technique is used to identify an in-focus focal“base” plane for the current slide. The base plane is identified byanalyzing images generated in the same manner that the images used toidentify the base planes in the model were generated. For example, ifthe base planes in the model were identified by analyzing gray scaleimages, then the scan component analyzes gray scale images of thecurrent slide to determine the base plane for the current slide. Inblocks 520-545, the component loops through each of the color channels(or filter bands) to capture a corresponding image for each. In block525, the offset for the current color channel (or filter band) stored bythe model is determined. In block 530, the component adjusts the focalplane based on the “base” plane determined in block 515 and the offset.For example, if the determined “base” plane is at 3.2 μm and the offsetis −1.1 μm, then the component will adjust the focal plane to 2.1 μm. Inblock 535, the component captures an image of the slide using theadjusted focal plane and the current color channel (or filter band). Inblock 540, the captured image is stored. In block 545, the next colorchannel (or filter band), if any, is selected and the component thenloops back to process the next color channel (or filter band). In block550, the component selects the next slide position, if any, and thenloops back to process the next slide position. The component thenreturns the captured image data for further processing and analysis.

FIG. 6 is a flow diagram illustrating the processing of the Z-scancomponent 240 for generating images for a slide based on a previouslygenerated auto-focus model, such as the auto-focus model generated bythe Z-calibrate. In block 605, the component generates Z-slices for thecurrent slide. In block 610, slide positions are determined based on themodel. Using the model of Table 2 as an example, the component mayidentify the portions of the slide corresponding to each position in the3×3 grid by splitting the slide into 9 portions corresponding to the 3×3grid. In some embodiments, the model may include additional informationabout the location of each portion if, for example, the portions are notthe same size, which the Z-scan component may use to determine the slidepositions. In blocks 615-675, the component loops through each of thedetermined slide positions to capture one or more images for each slideposition. In block 620, the generated Z-slices are analyzed to identifythe Z-slice having the sharpest image. The base Z-slice is identified byanalyzing images generated in the same manner that the images used toidentify the base Z-slices in the model were generated. For example, ifthe base Z-slices in the model were identified by analyzing gray scaleimages, then the Z-scan component analyzes gray scale images of thecurrent slide to determine the base Z-slice for the current slide. Asanother example, if the base Z-slices in the model were identified byanalyzing red channel images, then the Z-scan component analyzes redchannel images of the current slide to determine the base Z-slice forthe current slide. In blocks 625-670, the component loops through eachof the color channels (or filter bands) to capture a corresponding imagefor each. In block 630, the component determines the offset for thecurrent color channel (or filter band) stored by the model. In block635, the component determines the offset Z-slice based on the baseZ-slice determined in block 620 and the determined offset. For example,if the determined “base” Z-slice has an index of 7 and the offset is -2,then the component will identify the Z-slice corresponding to an indexof 5. In block 640, the component determines a sharpness of the baseZ-slice using a focus sharpness measure, such as the sum of absolutedifferences between an image and the same image shifted (e.g., shifted afew pixels in one direction), the sum of absolute differences between animage and the result of filtering the imaging with a smoothingoperation, a focus sharpness measure extracted after filtering the imagewith a multitude of smoothing operations at different filter scales, orany combination thereof In block 645, the component determines asharpness of the offset Z-slice. In decision block 650, if the sharpnessof the base Z-slice is greater than the sharpness of the offset Z-slice,then the component continues at block 655, else the component continuesat block 665. In block 655, the base Z-slice is selected as the imagedata for the current slide position and color channel (or filter band).In this manner, if the sharpness of the offset Z-slice is less than thesharpness of the base Z-slice, then the sharper Z-slice will beselected. In block 660, the component optionally updates the model toadjust the offset for the current slide position and color channel (orfilter band). For example, each time a particular model is used toanalyze slides, the component may record the index of the Z-slice thatis selected for each slide position and color channel (or filter band)pair and use this information to calculate an average when updating themodel. For example, an average (e.g., weighted average) of the previous5, 10, 15, or 100 Z-slice indices can be used to update the model. Inblock 665, the component selects the offset Z-slice as the image datafor the current slide position and color channel (or filter band). Inblock 670, the next color channel (or filter band), if any, is selected,and the component then loops back to process the next color channel (orfilter band). In block 675, the next slide position, if any, isselected, and the component then loops back to process the next slideposition. The component then returns the selected image data for furtherprocessing and analysis.

FIG. 7 is a block diagram illustrating the processing of a testcomponent 250 for determining whether a previously-generated model needsto be updated and, if so, updates the model, in accordance with someembodiments. In block 705, the component invokes the Z-calibratecomponent to generate a new model based on a received slide. In block710, the component stores the new model. In block 715, slide positionsare determined by the component. In blocks 720-740, the component loopsthrough each slide position to determine offset differences between thenew model and the previously-generated model. In blocks 725-735, thecomponent loops through each color channel (or filter band). In block730, the difference between the offset for the current position andcolor channel (or filter band) in the new model are determined, and thecomponent determines an offset for the current position and colorchannel (or filter band) in the previously-generated model. In block735, the component selects the next color channel (or filter band), ifany, and then loops back to process the next color channel (or filterband). In block 740, the next slide position, if any, is selected, andthe component then loops back to process the next slide position. Inblock 745, the component calculates a model difference valuecorresponding to the distance between the two models. For example, adifference value is determined by calculating the average of the offsetdifferences determined in block 730. As another example, each model canbe a vector of offsets and calculate a distance between the two based onthe square root of the sum offset differences squared (e.g.,

$\left. \sqrt{\sum\limits_{N}\left( {{offset}\mspace{14mu} {difference}} \right)^{2}} \right)$

where N represents the number of slide position and color channel (orfilter band) pairs and offset difference represents the offsetdetermines calculated in block 730 for a particular slide position andcolor channel (or filter band) pair. In decision block 750, if thedetermined model difference value is greater than a predeterminedthreshold, then the component continues at block 755, else the componentcompletes. In block 755, the model is updated by, for example, replacingthe previously-generated model with the new model, taking an average(e.g., weighted average) of previously-calculated offsets for the datecorresponding to the model, and so on.

FIGS. 8A-8E are images at various Z-slices or focal planes generated fora particular slide in some embodiments. The specimen in this example isstained with a Dual color ISH (in situ hybridization) method, and thegoal is to detect and classify dots, which are indicators of a specificgene expression within tumor cells by chromogenic marking of thespecific gene within the nucleus. In ISH, a labeled complementary DNA orRNA strand is used to localize a DNA/RNA sequence, which in turn acts asan indicator of chromosomal structure. It may be desirable to use afocus metric that considers the sharpness of the dots and is adapted tospecimens and staining methods where dot detection is a relevant part ofthe image analysis. For this image data, the relevant structures in theimage are the larger blue blobs and the small black and red dots. Insome embodiments, a focus sharpness measure can be employed that isspecialized for the specimen on the microscope slides and the stainingmethod that was applied to the specimen before imaging. For this imagedata, the focus can be chosen to find the sharpest representation forthe blue blobs, red dots, and black dots, and respective focus sharpnessmeasures can be applied. A method for enhancing the contribution to thefocus sharpness metric from somewhat round features (e.g., dot-like ordisk-like shapes) in the image(s) is to base the computation of themetric on the response of a method referred to in image processingliterature as using a radial symmetry operator or directional gradientconcentration filter. Example methods to detect round dots of a knowntarget size range are disclosed in Q. Yang, and B. Parvin, “Perceptualorganization of radial symmetries,” in Proceedings of: Computer Visionand Pattern Recognition, Volume 1, (2004); G. Loy and A. Zelinsky, “Fastradial symmetry for detecting points of interest,” IEEE

Transactions on Pattern Analysis and Machine Intelligence, Volume 25,Issue 8, pp. 959-973 (2003); and O. Schmitt and M. Hasse, “Radialsymmetries based decomposition of cell clusters in binary and gray levelimages,” Pattern Recognition, Volume 41, pp. 1905-1923 (2008). Once dotsare identified, a focus sharpness measure can be computed from thesharpness of all individually identified dots. The image gradient overthe dot boundary can be indicative of the sharpness of one dot. Methodsto detect dots in an image typically require the choice of parameters,such as a minimum radius and a maximum radius, and can be adapted todifferent tissue types and staining methods of the specimen on themicroscope slide. The focus sharpness metric can be based on theresponse of applying the filter once, or applying it a number of timeswith different parameters and combining the results. FIGS. 8A-8Eillustrate how different Z-slices of a slide or images captured atdifferent focal planes may have varying degrees of sharpness throughoutthe entire image and in specific regions. For example, blob 810 getssharper from FIG. 8A to FIG. 8B and then to FIG. 8C but then losessharpness in FIG. 8D and again in FIG. 8E. As another example, blob 820gets sharper from FIG. 8A to FIG. 8B to FIG. 8C and to FIG. 8D but thenloses sharpness in FIG. 8E. The techniques disclosed herein can be usedto produce focused color image of FIG. 8C.

The imaging techniques disclosed herein can be used to producehighly-focused images of different types of samples. The samples can bebreast tissue, such as that obtained during a needle biopsy, lumpectomy,or mastectomy. The samples can also be obtained from livingmulti-cellular vertebrate organisms, a category that includes human andnon-human mammals, such as veterinary subjects. The disclosed techniquescan be implemented different types of imaging systems that include,without limitation, a central processing unit, memory, input devices(e.g., keyboard and pointing devices), output devices (e.g., displaydevices), and memory and/or storage devices (e.g., disk drives). Forexample, the imaging apparatus 110 of FIG. 1 can include one or moreprocessing units, memory, etc. The memory and storage devices can becomputer-readable media that may be encoded with computer-executableinstructions that implement the technology, e.g., a computer-readablemedium that contains the instructions. The instructions can be storedand executed to perform a calibration process, scanning processes,recalibration process. In the calibration process, the instructions canbe executed to determine a Z-offset from a best focus plane for channelsthat provide a best focus plane in each of the channels. Thedeterminations can be stored in memory. In the scanning process, theinstructions can be executed to determine a best focus plane for a fieldof view of the digital imager 111 of FIG. 1. The best focus planeinformation can be stored in memory 112 of FIG. 1. Instructions can beexecuted to command the imager 111 of FIG. 1 to obtain image data in itsfield of view in each of the channels in accordance with the Z-offsetsdetermined in the calibration processes. In addition, the instructions,calibration information, data structures, and message structures may betransmitted via a data transmission medium, such as a signal on acommunications link and may be encrypted. Accordingly, computer-readablemedia include computer-readable storage media 112 upon which data can bestored and computer-readable transmission media upon which data can betransmitted. The data can include, without limitation, auto-focusroutines or techniques, calibration slide data (or other types ofreference data), reference images, scanning techniques, calibrationtechniques, or the like.

Many embodiments of the technology described herein may take the form ofcomputer-executable instructions, including routines executed by aprogrammable computer. For example, the analyzing system 100 of FIG. 1can have computer-executable instructions for performing the calibrationprocesses of FIGS. 3 and 4. The memory 112 of FIG. 1 can store theexecutable instructions. Those skilled in the relevant art willappreciate that aspects of the technology can be practiced on computersystems other than those shown and described herein. Embodiments of thetechnology may be implemented in and used with various operatingenvironments that include personal computers, server computers, handheldor laptop devices, multiprocessor systems, microprocessor-based systems,programmable consumer electronics, digital cameras, network PCs,minicomputers, mainframe computers, computing environments that includeany of the above systems or devices, and so on. Moreover, the technologycan be embodied in a special-purpose computer or data processor that isspecifically programmed, configured or constructed to perform one ormore of the computer-executable instructions described herein.Accordingly, the terms “computer” or “system” as generally used hereinrefer to any data processor and can include Internet appliances andhandheld devices (including palmtop computers, wearable computers,cellular or mobile phones, multi-processor systems, processor-based orprogrammable consumer electronics, network computers, mini computers andthe like). Information handled by these computers can be presented atany suitable display medium, including a CRT display or LCD. A user canview images and scores on such displays.

From the foregoing, it will be appreciated that specific embodiments ofthe technology have been described herein for purposes of illustration,but that various modifications may be made without deviating from thedisclosure. The facility can include additional components or features,and/or different combinations of the components or features describedherein. Moreover, while the techniques described above are generallydescribed in the context of slide analysis, these techniques can beemployed to enhance auto-focus techniques in different types ofscanners, imagers, cameras, etc. Additionally, while advantagesassociated with certain embodiments of the new technology have beendescribed in the context of those embodiments, other embodiments mayalso exhibit such advantages, and not all embodiments need necessarilyexhibit such advantages to fall within the scope of the technology.Accordingly, the disclosure and associated technology can encompassother embodiments not expressly shown or described herein. The followingexamples describe additional embodiments of the technology disclosedherein.

1. A method for acquiring focused images of a microscope slide, themethod comprising: in a calibration step, determining a Z-offset from abest focus plane for each of multiple color channels of a color digitalimager that provides a best focus plane in each of the color channels;in a scanning step, determining a best focus plane for a field of viewof the color digital imager; and obtaining image data in the field ofview with the color digital imager in each of the color channels inaccordance with the Z-offsets determined in the calibration step.
 2. Themethod of claim 1, wherein the Z-offsets vary depending on the alocation of a slide region being imaged by the color digital imager. 3.The method of claim 1, wherein the Z-offsets are obtained in thecalibration step from one or more training slides.
 4. The method of anyof claims 1, wherein the scanning step further comprises: obtainingimages in the color channels at the best focus plane; computing asharpness metric for the images acquired at the best focus plane and atthe Z-offset from the best focus plane; and selecting the image with anoptimum sharpness metric to output from the color digital imager.
 5. Themethod of claim 1, wherein the calibration step further comprises:performing a Z-slice scan of a calibration slide.
 6. The method of claim5, the scanning step further comprising: performing a Z-slice scan of aslide.
 7. A method for acquiring focused images of a microscope slideusing a microscope having an optical system and a digital color camera,the method comprising: characterizing chromatic aberration present inthe optical system as a Z-offset from a best focus plane in each ofmultiple color channels of the digital color camera; and scanning amicroscope slide in a manner to reduce the effect of the characterizedchromatic aberration by obtaining image data from the multiple colorchannels in accordance with the Z-offsets.
 8. The method of claim 7,wherein the characterizing is obtained from one or more calibrationslides.
 9. The method of claim 8, wherein the characterizing is obtainedfrom a Z-slice through a calibration slide.
 10. The method of claim 9,further comprising: adjusting the characterizing of the chromaticaberration during the scanning step.
 11. The method of claim 10, furthercomprising: acquiring images in the multiple color channels from themicroscope slide at a best focus plane; and comparing a focus metric ofthe multiple color channel images at the best focus plane with themultiple color channel images obtained by the scanning.
 12. The methodof claim 11, further comprising: updating the Z-offsets depending onresults of the comparing.
 13. A system, having a memory and a processor,the system comprising: a calibration component configured to determinean offset from a first focus plane for at least one of a color channelor a filter band; a base component configured to determine, for a firstslide, a base focus plane for a field of view of the first slide; and acapture component configured to retrieve the offset and obtain an imageof the first slide based at least in part on the base focus plane andthe retrieved offset; wherein at least one of the components comprisescomputer-executable instructions stored in the memory for execution bythe processor.
 14. The system of claim 13, wherein the calibrationcomponent is configured to determine, for each of a plurality of filterbands, an offset from the first focus plane that provides a best focusplane for the filter band.
 15. The system of claim 14, wherein thecapture component is configured to retrieve, for each of the pluralityof filter bands, the offset determined for the filter band.
 16. Thesystem of claim 15, wherein the capture component is configured toobtain, for each of the plurality of filter bands, an image based atleast in part on the base focus plane and the offset determined for thefilter band.
 17. The system of claim 16, wherein each obtained image ispreviously-captured z-slice.
 18. The system of claim 13, wherein thecalibration component is configured to determine, for each of aplurality of color channels, an offset from the first focus plane thatprovides a best focus plane for the color channel.